Further Investigation Of High Electrical Breakdown For Water Dielectric

Development of HPM (high power microwave) requires high power pulse conditioning system with high output power, small volume, and wide application range. Water dielectric, because of its great dielectric constant and high breakdown stress, is extensively used as the energy storage medium in high power pulse conditioning system. So methods of pressurization, surface polish, and glycol additive are mainly applied to improve electrical breakdown strength of water dielectric. Based on the systemic research on water breakdown and on recovery of water charged, dependence of water breakdown stress on hydrostatic pressure, level of surface polish, and glycol concentration is obtained and a minimum time interval for water charged normally is achieved. Research results indicate a good future of application of water pulse power conditioning system. Contents are shown as follows:Firstly, high electrical breakdown for pressurized water dieletric is investigated. An experimental apparatus with test cell of coaxial electrodes is set up. High electrical breakdown experiments for water dielectric and for pressurized water dielectric are carried out with microsecond charging, respectively. Experimental results and analyses have qualitatively verified Mirza theory that water breakdown stress is increased with hydrostatic pressure to the one eighth power. And additional magnitude of 31.5% is observed when the hydrostatic pressure increases from 1atm to 11atm. The increase of breakdown stress for pressurized water is explained with bubble breakdown predicted by Jones and Kunhardt. And results are compared with other results on pressurization effect of water dielectric. Reason resulting in ineffectiveness of pressurization to improve water breakdown stress in short charging time is given.Secondly, influence of surface polish and glycol additive on pressurized water dielectric is studied. For different surface roughness of electrodes and glycol concentration of glycol/water mixture, pressurized water breakdown experiments are carried out. Experimental results suggest that Mirza's formula is valid and independent of surface roughness and glycol concentration, and it is accumulative for surface polish, glycol additive, and pressurization for the capability to improve electrical breakdown strength. Moreover, the increase of electrical breakdown strengthof water dielectric for surface polish is explained with bubble breakdown. Especially, highest stress of 235.5kV/cm observed in glycol/water mixture with a glycol concentration of 80% at a hydrostatic pressure of 12atm is about one time greater than that in pure water at constant pressure.Finally, to study the influences of rolling state on breakdown and of non-grouded state on charging, water breakdown experiment in the rolling state at low speed and non-grounded HPM system experiment are carried out, respectively. Experimental results indicate that breakdown stress in the rolling state at low speed is a little higher than that in the static state and non-grounded state has no influence on charging of water dielectric. The possible mechanism is that the number of bubbles near the surface of electrodes is reduced in the rolling state.